The invention is directed to an apparatus for determining a rotation rate, with an oscillatory body on which a plurality of electromechanical converters are mounted, of which at least a first converter is caused to oscillate mechanically by an electric driver signal generated in a first circuit arrangement, and at least a second converter is caused to oscillate mechanically by an electric damping signal generated in a second circuit arrangement, and at least a third converter emits an electric sensor damping signal which corresponds to the oscillation of the body in the location where the at least third converter is mounted ,the sensor damping signal being fed back to the input of the second circuit arrangement.
This type of apparatus which generally works according to the principle of a vibration gyrometer is known, for example, from DE-44 47 005 A1. The electromechanical converters present in the apparatus, generally piezo-electric elements, evaluate the effect of the Coriolis acceleration which serves as a measure for a rotation rate at which the oscillatory body rotates. This known apparatus is therefore well suited for use in connection with systems for controlling driving dynamics in motor vehicles, since the detected Coriolis acceleration can be used as a measure for the current yaw rate of the vehicle.
In the case of the known apparatus, the oscillatory body is realized as a thin-walled hollow cylinder made from an elastic material. On the cylinder wall, eight piezo-elements are arranged at a uniform distance of 45 degrees relative to one another. The piezo-elements arranged, for example, at the positions of 0 degrees, 90 degrees, 180 degrees and 270 degrees work together with an oscillator stage. The piezo-elements arranged in the positions of 45 degrees, 135 degrees, 225 degrees and 315 degrees work together with a damping stage. The piezo-elements arranged in the positions of 0 and 180 degrees are caused to oscillate mechanically by an oscillator driver stage. The piezo-elements arranged in the positions at 90 and 270 degrees emit a signal which corresponds to the oscillation of the hollow cylinder in the location where the piezo-elements are arranged. The signal emitted by the piezo-elements arranged in the 90-degree and 270-degree positions is fed back to the input of the circuit arrangement for generating the electric oscillator driver signal in such a way that this results in an oscillator oscillating at its resonant frequency.
The hollow cylinder is oscillated by the piezo-electric elements which are arranged at the positions of 0 and 180 degrees and which are mechanically oscillated by the oscillator driver stage. The hollow cylinder oscillates in such a way that nodal points form at the positions of 45 degrees, 135 degrees, 225 degrees and 315 degrees when it is in a steady state. If a rotation rate acts on the hollow cylinder from outside, the steady state of the hollow cylinder is disturbed because of the Coriolis acceleration. The system is detuned in such a way that the position of the nodal points shifts. Because of this, the hollow cylinder carries out oscillations in the locations where the nodes were previously.
The piezo-elements arranged in the 45-degree and 225-degree positions can be oscillated mechanically using a damping driver stage. The piezo-elements arranged in the positions of 135 degrees and 315 degrees emit a signal which corresponds to the oscillation of the hollow cylinder at the location where they are arranged. The signal emitted by the piezo-elements arranged in the positions of 135 and 315 degrees is fed back to the input of the circuit arrangement which is provided for the excitation of the piezo-elements arranged in the positions of 45 degrees and 225 degrees in such a way that the oscillations in the positions of 135 degrees and 315 degrees are compensated approximately to zero.
The voltage fed back to the input of the circuit arrangement for the excitation of the piezo-elements arranged in the positions of 45 degrees and 225 degrees is a measure of the detuning of the hollow cylinder caused by the effect of a rotation rate on the oscillating hollow cylinder. This signal can therefore be used as a measure of the rotation rate.
For adaptation to a circuit arrangement for further processing of the signal, the known apparatus provides an amplifier with adjustable amplification. Although the output signal of the known apparatus can be adjusted by the amplifier, the known apparatus has the disadvantage that it does not provide for the possibility of tuning or balancing the circuit with respect to the tolerances of the component parts. This has disadvantageous results especially when, as provided in the known circuit arrangement, the possibility is provided for adding an interference signal by means of which the perfect functioning of the circuit arrangement is tested in a so-called self-test.
In order to carry out the self-test, the signal which is emitted by the piezo-elements arranged in the positions of 90 degrees and 270 degrees and which is fed back to the input of the oscillator driver stage is guided to an amplifier and guided via a switch to the input of the damping driver stage provided for the excitation of the piezo-elements arranged in the positions of 45 degrees and 225 degrees. This detunes the system in the same manner as is effected under the effect of a rotation rate. Since the magnitude of the self-test signal is determined, the output signal must reach a certain magnitude because of the detuning if the apparatus is working correctly. If this is not the case, it indicates that the apparatus is not working properly.
Since the output signal which is generated because of the interference signal is supposed to correspond to a predetermined rotation rate and be independent of the adaptation carried out by the output amplifier, the amplifier for generating the self-test signal can also be adjusted with respect to its amplification. The independence of the output signal from the adaptation effected by the output amplifier is achieved in that the inputs of the amplifier for adjusting the amplification are coupled together and work in opposite directions.
Tolerances of component parts cannot be compensated for, however, by adapting the self-test signal by means of the amplifier which is adjustable with respect to amplification. In particular, differences between the dynamic systems behavior or transient response of the piezo-elements of the damping stage and the piezo-elements of the oscillator stage cannot be compensated for by adjusting the self-test signal.
However, as regards the self-test, a perfect functioning of the known circuit arrangement is only guaranteed if the transient responses are identical so that they cancel each other. Since this is not the case in practice, an incorrect self-test value is obtained. A correspondingly large expenditure on circuitry is required in order to overcome this problem. Adapting the transient response to an integrated circuit, the known circuit arrangement generally being constructed as such, is overridden by the process parameters of semiconductor production and is therefore difficult to do with the desired accuracy. In the case of the known circuit arrangement, a systematic correction is therefore effected by two capacitive voltage dividers of different values in the hybrid circuit following the circuit arrangement. However, this is disadvantageous because this step has a temperature response made up of the transient response and the capacitive voltage divider.
It is the object of the present invention to construct an apparatus of the type mentioned in the beginning in such a way that it can be tuned in a simple manner.
This object and others which will be made more apparent hereinafter are attained in an apparatus for determining a rotation rate, with an oscillatory body on which a plurality of electromechanical converters are mounted, of which at least a first converter is caused to oscillate mechanically by an electric driver signal generated in a first circuit arrangement, and at least a second converter is caused to oscillate mechanically by an electric damping signal generated in a second circuit arrangement, and at least a third converter emits an electric sensor damping signal which corresponds to the oscillation of the body in the location where the at least third converter is mounted, the sensor damping signal being fed back to the input of the second circuit arrangement.
According to the invention, there is provided a voltage divider by means of which the signal generated in the second circuit arrangement can be reduced. It has been shown that the transient response of the piezo-elements of the damping stage is always stronger than that of the piezo-elements of the oscillator stage. The signal for generating the self-test signal which has been decoupled from the oscillator stage must therefore be compensated for by a typically weaker output signal from the damping driver stage. The output signal of the circuit arrangement obtained because of the self-test signal therefore always deviates from the true value by being lower.
If the signal to the piezo-elements of the damping stage in the positions of 45 degrees and 225 degrees is reduced, the circuit arrangement for generating the signal required for the excitation of the piezo-elements arranged in the positions of 45 degrees and 225 degrees must supply an output voltage that is higher than it would have to be if the signal had not been reduced. Accordingly, the output signal of the circuit arrangement according to the invention is increased so that its value corresponds to the self-test signal that is fed in.
Accordingly, it is possible to adapt the output signal of the apparatus for determining a rotation rate to the self-test signal by changing the signal provided for the excitation of the damping stage. It is particularly advantageous that the adaptation can be done using a resistive voltage divider. This has a very positive effect on the temperature response of the apparatus. Further, it is very advantageous that the voltage divider is in the low-impedance driver circuit and not in the high-impedance sensor circuit. Since the adaptation is carried out by the entire circuit arrangement, all of the tolerances affecting the self-test signal can be compensated for in this way. In a particularly advantageous manner, the voltage division is carried out using a potentiometer.
In a special embodiment form of the invention, circuit elements are provided by means of which an interference signal is guided to the input of the second circuit arrangement. By mean of this interference signal, a self-test of the apparatus according to the invention can be carried out in an advantageous manner. It is particularly advantageous in the circuit according to the invention that the output signal generated because of the interference signal can be adjusted easily using the voltage divider.
In another embodiment form of the apparatus according to the invention, at least a fourth electromechanical converter is provided which emits a sensor driver signal corresponding to the oscillation of the body at the location where the at least fourth converter is arranged, in which case the sensor driver signal is guided back to the input of the first circuit arrangement and the interference signal corresponds to a part or a multiple of the sensor driver signal that is guided back to the input of the first circuit arrangement. Since the interference signal is obtained from the oscillator circuit, its frequency corresponds at all times exactly to the frequency at which the oscillatory body is oscillating. It can therefore be adapted optimally to the input of the second circuit arrangement.